Infrared detecting device

ABSTRACT

An infrared detecting device. The device includes a drive power supply circuit which supplies a drive current to each of signal circuits comprised of an I/V conversion circuit, a voltage amplification circuit, a detection circuit and an output circuit. The drive power supply circuit is comprised of a current generating circuit and a distribution circuit. The current generating circuit includes a reference current source, a fixed current source which provides a fixed current based on reference current and a variable current source which provides a variable current stepped up or down to any of different currents based on the reference current. The distribution circuit distributes the drive current to a part of the signal circuits based on the current from the fixed current source and distributes the drive current to a remaining part of the signal circuits based on the current from the variable current source. The device reduces current consumption while keeping the performance or behavior of the circuits in stable state.

TECHNICAL FIELD

The invention relates an infrared detecting device.

BACKGROUND ART

Infrared detecting devices are specially used in different electricalproducts which efficiently save energy while detecting a human body.

A prior art device described Japanese Patent Publication No. 11-83624 iscomprised of a pyroelectric element, an I/V conversion circuit, avoltage amplification circuit, a detection circuit and an outputcircuit. The pyroelectric element is operable to generate a microcurrent signal in response to variation of incoming infrared radiationfrom detection area through condenser lens or the like. The I/Vconversion circuit converts the current signal from the pyroelectricelement into a voltage signal. The voltage amplification circuitselectively amplifies components with prescribed frequencies of thevoltage signal to issue a components-amplified voltage. The detectioncircuit is comprised of, for example, a window comparator and provides acomparison between the components-amplified voltage and a prescribeddetection threshold voltage to issue a detection signal of the infraredradiation. The detection threshold voltage is a window threshold with ahigher threshold voltage and a lower threshold voltage. The outputcircuit is comprised of, for example, level shift circuit or the likeand issues an output signal in response to the detection signal. Thisinfrared detecting device issues the output signal for representingdetection of the infrared radiation (e.g., human body) when thecomponents-amplified voltage is less or more than the window thresholdrange. The device also issues the output signal for representingnon-detection of the infrared radiation when the components-amplifiedvoltage is converged within the window threshold range.

A prior art device described Japanese Patent Publication No. 2002-156281comprises a battery as a power source in addition to the pyroelectricelement, the I/V conversion circuit, the voltage amplification circuit,the detection circuit and the output circuit. This infrared detectingdevice provides a rated current as a drive current to I/V conversioncircuit, the voltage amplification circuit, the detection circuit andthe output circuit when voltage of the I/V conversion circuit exceeds aprescribed voltage. When the voltage of the I/V conversion circuit isequal to or lower than the prescribed voltage, the device provides asmaller current than the rated current as the drive current to thosecircuits. In this case, current consumption (drive current) can bereduced.

However, in the construction that reduces current consumption as thedevice does, there is a problem that the performance or behavior of thecircuits become unstable. Because the circuits will easily sufferdispersion of parts-performance such as threshold of transistors,resistance and capacitance, or dispersion of current consumption causedby temperature characteristics. There is also a trend that indicatesgreater dispersion of the current consumption in case the drive currentto the circuits is much reduced to the level such as, for example, 10 snA below a few μA. Considering these issues, since there is a need ofdesign with sufficient allowance for power voltage, temperaturecharacteristics, dispersion of parts-performance or the like in order toprovide infrared detecting devices with low consumption, it is difficultto sufficiently save energy of the device.

DISCLOSURE OF THE INVENTION

An object of the present invention is to reduce current consumptionwhile keeping the performance or behavior of the circuits in stablestate.

An infrared detecting device of the present invention comprises apyroelectric element, an I/V conversion circuit, a voltage amplificationcircuit, a detection circuit, an output circuit and a drive power supplycircuit. The pyroelectric element generates a current signal based onincoming infrared radiation. The I/V conversion circuit converts thecurrent signal into a voltage signal. The voltage amplification circuitselectively amplifies components with prescribed frequencies (prescribedfrequencies components) of the voltage signal to issue acomponents-amplified voltage. The detection circuit provides acomparison between the components-amplified voltage and a prescribeddetection threshold voltage to issue a detection signal of the infraredradiation. The output circuit issues an output signal based on thedetection signal. The drive power supply circuit supplies a drivecurrent to each of signal circuits comprised of the I/V conversioncircuit, the voltage amplification circuit, the detection circuit andthe output circuit. As characteristic of this invention, the drive powersupply circuit is comprised of a current generating circuit and adistribution circuit. The current generating circuit includes areference current source, a fixed current source and a variable currentsource. The reference current source generates a reference current. Thefixed current source provides a fixed current based on the referencecurrent. The variable current source provides a variable current varyingwith the reference current. The distribution circuit distributes thedrive current to a part of the signal circuits based on the current fromthe fixed current source. The distribution circuit also distributes thedrive current to the remaining part of the signal circuits based on thecurrent from the variable current source.

By distributing the drive current to the part of the signal circuitsbased-on the current from the fixed current source, influence of currentchangeover in the part can be excluded and therefore the performance orbehavior of the part can be kept in stable state. By distributing thedrive current to the remaining part based on the current from thevariable current source, current consumption of the remaining part canbe reduced.

The drive power supply circuit may comprise a plural of the variablecurrent source, each of which is individually connected to each circuitof the remaining part of the signal circuits. In this case, since thedrive current to each of the remaining part can be individually changed,the drive current can be preferably reduced to low level.

The drive power supply circuit may comprise a terminal for receiving achangeover signal. The variable current source may step the variablecurrent up or down to any of prescribed different currents in accordancewith the changeover signal received at the terminal. Since drive currentcan be changed over in accordance with the changeover signal, currentconsumption can be adaptively reduced.

The variable current source may step the variable current up or down toany of prescribed different currents based on variation of powervoltage. In this case, the drive current can be preferably reduced basedon the variation of the power voltage.

The variable current source may step the variable current up or down toany of prescribed different currents based on variation in ambienttemperature. In this case, the drive current can be preferably reducedbased on the variation in ambient temperature.

The voltage amplification circuit may comprise a differential stage andan output stage. The distribution circuit may distribute the drivecurrent to the differential stage or the output stage based on thecurrent from said variable current source, or distribute same ordifferent current as the drive current to the differential stage and theoutput stage based on the current from said variable current source.

The infrared detecting device may further comprise a suppression circuitand the drive power supply circuit may comprise a current changeovercircuit. This current changeover circuit provides a first changeoversignal to the variable current source when the components-amplifiedvoltage is closer to a reference level than a transition thresholdvoltage. This transition threshold voltage is set to be closer to thereference level than the detection threshold voltage. The currentchangeover circuit also provides a second changeover signal to thevariable current source when the components-amplified voltage is furtherfrom the reference level than the transition threshold voltage. Thevariable current source steps the variable current down to a currentsmaller than a rated current of prescribed different currents based onthe first changeover signal. The variable current source also steps thevariable current up to the rated current based on the second changeoversignal. The suppression circuit starts suppression of output of anycircuit or circuits included in the signal circuits in order to suppressthe output signal of the output circuit. The suppression is started froma start point in time on or before which the variable current sourcesteps up or down the variable current. The suppression circuit alsoreleases the suppression after a prescribed time period. In this case,it becomes possible to prevent false operation due to variation when thedrive current is changed over.

The suppression circuit may comprise a resistor, a constant voltagesupply circuit, a switch and a switch controlling circuit. The resistoris connected in series between the voltage amplification circuit and thedetection circuit. The constant voltage supply circuit supplies aconstant voltage between the resistor and the detection circuit throughthe switch. The switch is connected between from the constant voltagesupply circuit to the resistor and the detection circuit. The switchalso opens or closes a pathway from the constant voltage supply circuitto the resistor and the detection circuit in response to OFF or ONsignal from the switch controlling circuit respectively. The switchcontrolling circuit provides the ON signal to the switch from the startpoint. The switch controlling circuit also provides the OFF signal tothe switch after the time period.

The voltage amplification circuit may comprise an operational amplifierand a feedback resistor, and the suppression circuit may comprise aswitch and a switch controlling circuit. The operational amplifier has apositive input terminal, a negative input terminal and an outputterminal. The feedback resistor is connected between the output terminaland one of the input terminals. The switch is connected in parallel withthe feedback resistor. The switch also opens or closes its parallelpathway in response to OFF or ON signal from the switch controllingcircuit respectively. The switch controlling circuit provides the ONsignal to the switch from the start point. The switch controllingcircuit also provides the OFF signal to the switch after the timeperiod. Since output of the voltage amplification circuit is suppressedat 1× input voltage of the voltage amplification circuit during the timeperiod, it becomes possible to prevent false operation due to variationwhen the drive current is changed over.

The suppression circuit may comprise a resistor, a switch, a constantvoltage supply circuit and a switch controlling circuit. The switch isconnected between the voltage amplification circuit and the detectioncircuit. The switch also opens or closes a pathway from the voltageamplification circuit to the detection circuit in response to OFF or ONsignal from the switch controlling circuit respectively. The constantvoltage supply circuit supplies a constant voltage between the switchand the detection circuit through the resistor. The switch controllingcircuit provides the OFF signal to the switch from the start point. Theswitch controlling circuit also provides the ON signal to the switchafter the time period. Since the pathway is opened during the timeperiod, it becomes possible to prevent false operation due to variationwhen the drive current is changed over.

The suppression circuit may comprise a constant voltage supply circuit,a switch and a switch controlling circuit. The constant voltage supplycircuit supplies a constant voltage to the detection circuit through theswitch. The switch is connected between from the constant voltage supplycircuit and the voltage amplification circuit to the detection circuit.The switch also closes or opens a pathway (hereinafter referred to as a“first pathway”) between the constant voltage supply circuit and thedetection circuit in response to suppression or unsuppression signalfrom the switch controlling circuit respectively. The switch also opensor closes a pathway (hereinafter referred to as a “second pathway”)between the voltage amplification circuit and the detection circuit inresponse to the suppression or the unsuppression signal respectively.The switch controlling circuit provides the suppression signal to theswitch from the start point. The switch also provides the unsuppressionsignal to the switch after the time period. Since the first and thesecond pathways are closed and opened during the time period, it becomespossible to prevent false operation due to variation when the drivecurrent is changed over.

The suppression circuit may comprise a switch and a switch controllingcircuit. The switch is connected between the detection circuit and theoutput circuit. The switch also opens or closes a pathway between thedetection circuit and the output circuit in response to OFF or ON signalfrom the switch controlling circuit respectively. The switch controllingcircuit provides the OFF signal to the switch from the start point. Theswitch controlling circuit also provides the ON signal to the switchafter the time period. Since the pathway is opened during the timeperiod, it becomes possible to prevent false operation due to variationwhen the drive current is changed over.

The switch controlling circuit may issue the second changeover signal sothat the variable current source increases the variable current to thebiggest rated current while stepping up from smallest current of thedifferent currents according to the second changeover signal. The switchcontrolling circuit may also issue the first changeover signal so thatthe variable current source decreases the variable current to thesmallest current while stepping down from the rated current of thedifferent currents according to the first changeover signal. Since thevariable current is increased or decreased by sequential step up or down(i.e. discrete up or down) operation which can reduce variation itbecomes possible to preferably prevent false operation due to variationwhen the drive current is changed over.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described in furtherdetails. Other features and advantages of the present invention willbecome better understood with regard to the following detaileddescription and accompanying drawings where:

FIG. 1 is an electrical diagram of an infrared detecting device of afirst embodiment according to the present invention;

FIG. 2 is an electrical diagram of a voltage amplification circuit inthe arrangement of FIG. 1;

FIG. 3 is an electrical diagram of an operational amplifier in thearrangement of FIG. 2;

FIG. 4 is a graph of reference current in the operational amplifierversus variation of power voltage;

FIG. 5 is an electrical diagram of an alternate embodiment;

FIG. 6 is an electrical diagram of an infrared detecting device of asecond embodiment according to the present invention;

FIG. 7 is an electrical diagram of a current changeover circuit, acurrent generating circuit and a distribution circuit in the arrangementof FIG. 6;

FIG. 8 is an electrical diagram showing a part of an infrared detectingdevice of a third embodiment according to the present invention;

FIG. 9 is a graph of current consumption versus variation of powervoltage in the device of FIG. 8;

FIG. 10 is a graph of current consumption of an alternate embodimentversus variation of power voltage;

FIG. 11 is an electrical diagram of an infrared detecting device of afourth embodiment according to the present invention;

FIG. 12 is a timing diagram showing operation of the device of FIG. 11;

FIG. 13 is an electrical diagram 11; showing a part of an infrareddetecting device of a fifth embodiment according to the presentinvention;

FIG. 14 is an electrical diagram showing a part of an infrared detectingdevice of a sixth embodiment according to the present invention;

FIG. 15 is a timing diagram showing operation of a suppression circuitof the device of FIG. 14;

FIG. 16 is an electrical diagram showing a part of an infrared detectingdevice of a seventh embodiment according to the present invention;

FIG. 17 is an electrical diagram showing a part of an infrared detectingdevice of a eighth embodiment according to the present invention;

FIG. 18 is a timing diagram showing operation of an alternateembodiment;

FIG. 19 is an electrical diagram showing a part of an infrared detectingdevice of a ninth embodiment according to the present invention; and

FIG. 20 is a timing diagram showing operation of the device of FIG. 19.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an infrared detecting device A of a first embodimentaccording to the present invention.

The device A comprises a drive power supply circuit 10 as acharacteristic of the embodiment in addition to comprising apyroelectric element 15, an I/V conversion circuit 16, a voltageamplification circuit 17, a detection circuit 18 and an output circuit19 as well as the prior art devices.

By the way, the above-mentioned prior art device has a limitation inreduction of current consumption of circuits 16-19 in order to secure acertain additional coverage for the ability of current supply. Thispoint is explained in detail with reference to FIGS. 2 and 3.

The voltage amplification circuit 17 as shown in FIG. 2 comprises anoperational amplifier 170 and resistors 171 and 172. The amplifier 170has a positive input terminal, a negative input terminal and an outputterminal. A reference voltage Vref is applied to the positive inputterminal. The resistor (feedback resistor) 171 is connected between thenegative input terminal and the output terminal. The resistor 172 isconnected between the I/V conversion circuit 16 and the negative inputterminal of the amplifier 170.

The amplifier 170 as shown in FIG. 3 is constructed with a differentialstage 170 a, an output stage 170 b and a constant current stage 170 c.This stage 170 c comprises transistors 170 d-170 i which constructmirror circuits. The stage 170 c also provides power to the differentialstage 170 a and output stage 170 b. The transistor 170 d is a PMOSdepletion type of transistor. Each of the transistors 170 f, 170 h and170 i is a PMOS enhancement type of transistor. Each of the transistors170 e and 170 g is a NMOS enhancement type of transistor. For example,the resistors 171 and 172 are set to 5 M Ohms and 200 K Ohmsrespectively, and thereby an voltage amplification rate of the amplifier170 is set to 25 times (5 M Ohms/200 K Ohms). The ratio of currentmirror of the stage 170 c is set in order that a reference current of200 nA flows into the transistor 170 d while a drive current 200 nA and400 nA flow into the stages 170 a and 170 b respectively, when powervoltage is 3 V.

In this construction, if the power voltage is reduced to 2V due to anycause, the current into the transistor 170 d as shown in FIGS. 3 and 4is reduced to approximately the half (from 200 nA to 100 nA). The outputcurrent ability of the amplifier 170 is also reduced to the half (from400 nA to 200 nA). Therefore, when input signal of the amplifier 170 isgreater than the upper end of the output current ability, the amplifier170 cannot amplify the input signal in accordance with the voltageamplification rate. As a result, the secureness of the additionalcoverage and the reduction of the current consumption appear to be acontradictory problem.

In order to solve this problem, the circuit 10 as shown in FIG. 1′comprises a current changeover circuit 11, a current generating circuit12 and a distribution circuit 13. The circuit 10 also supplies a drivecurrent to each of signal circuits comprised of circuits 16-19. Thiscircuit 10 is characterized by independent current mirror circuits whichare individually designed for the voltage amplification circuit 17, thedetection circuit 18 and the output circuit 19. And these current mirrorcircuits change the dive current for each of the circuits 17-19.

The current changeover circuit 11 issues changeover signals forchangeover of the dive current to the above-mentioned each circuit.

The current generating circuit 12 is comprised of a reference currentsource 120, a fixed current source 121 and variable current sources122-124. The circuit 12 generates a fixed current and variable currents.The reference current source 120 generates a reference current. Thefixed current source 121 is comprised of a current mirror circuit with aterminal T121. The source 121 provides the distribution circuit 13through the terminal T121 with the fixed current based on the referencecurrent from the reference current source 120. The variable currentsources 122-124 are comprised of current mirror circuits with terminalsT122-T124 respectively. Each variable current source provides thedistribution circuit 13 through its terminal with the variable currentstepped up or down to any of different currents based on the referencecurrent. For example, the different currents are set to one, two, threetimes of the reference current.

In an example of FIG. 1, the fixed current source 121 is constructedwith NMOS transistors 121 a and 121 b. The transistor 121 a is connectedbetween the reference current source 120 and ground. The transistor 121b is connected between the terminal T121 and ground. Gates of thesetransistors 121 a and 121 b are also connected each other, while thegates are connected to a drain of the transistor 121 a. This source 121provides to the distribution circuit 13 through the terminal T121′ witha current obtained by increasing or decreasing the reference current ata ratio of current mirror. This ratio of current mirror is decided by aratio (width/length) of transistor sizes of the transistors 121 a and121 b.

The variable current source 122 is constructed with NMOS transistors 122b, 122 c and 122 d and switch elements (e.g., PMOS transistors) 122 fand 122 g. The NMOS transistor 122 b is connected between the terminalT122 and ground, and its gate is connected to the drain and the gate ofthe NMOS transistor 121 a. The NMOS transistor 122 c is connected inseries with the switch element 122 f, while the series combination ofthe transistor 122 c and the element 122 f is connected between theterminal T122 and ground. A gate of the transistor 122 c is alsoconnected to the drain and the gate of the NMOS transistor 121 a. TheNMOS transistor 122 d is connected in series with the switch element 122g, while the series combination of the transistor 122 d and the element122 g is connected between the terminal T122 and ground. A gate of thetransistor 122 d is also connected to the drain and the gate of the NMOStransistor 121 a. Each transistor of this source 122 provides to thedistribution circuit 13 through the terminal T122 (and the switchelement) with a current obtained by increasing or decreasing thereference current at a ratio of current mirror. This ratio of currentmirror is decided by a ratio of transistor sizes of the transistor 121 aand itself (122 b, 122 c or 122 d).

The variable current source 123 is constructed with NMOS transistors 123b, 123 c and 123 d and switch elements 123 f and 123 g as well as thesource 122. The variable current source 124 is constructed with NMOStransistors 124 b, 124 c and 124 d and switch elements 124 f and 124 gas well as the source 122.

The distribution circuit 13 is comprised of current mirror circuits131-134 and distributes the drive current to a part of the signalcircuits, for example circuit 16 based on the current from the fixedcurrent source 121. The circuit 13 also distributes the drive current tothe remaining part of the signal circuits, for example circuits 17-19based on the current from the variable current sources 122-124.

In the example of FIG. 1, the circuit 131 is constructed with PMOStransistors 131 a and 131 b. The transistor 131 a is connected between avoltage source and the terminal T121. The transistor 131 b is connectedbetween the voltage source and the I/V conversion circuit 16. Gates ofthese transistors 131 a and 131 b are also connected each other, whilethe gates are connected to a drain of the transistor 131 a. This circuit131 obtains the drive current by increasing or decreasing the currentfrom the source 121 at a ratio of current mirror. And the circuit 131distributes the drive current to the I/V conversion circuit 16. Theratio of current mirror is decided by a ratio of transistor sizes of thetransistors 131 a and 131 b.

The circuit 132 is constructed with PMOS transistors 132 a and 132 b aswell as the circuit 131 and distributes the drive current based on thecurrent from the source 122 to the voltage amplification circuit 17. Thecircuit 133 is constructed with PMOS transistors 133 a and 133 b as wellas the circuit 131 and distributes the drive current based on thecurrent from the source 123 to the detection circuit 18. The circuit 134is constructed with PMOS transistors 134 a and 134 b as well as thecircuit 131 and distributes the drive current based on the current fromthe source 124 to the output circuit 19.

The operation of the infrared detecting device A is now explained. Inany of the variable current sources 122-124, when both of the switchelements turn off by the changeover signal from the current changeovercircuit 11, for example the current (hereinafter also referred to as the“generated current”) equivalent to the reference current is provided tothe distribution circuit 13 from the terminal. The distribution circuit13 then distributes the drive current (e.g., the current equivalent tothe reference current) based on the generated current to thecorresponding circuit of the circuits 17-19.

In any of the sources 122-124, when one of the switch elements turns onby the changeover signal from the circuit 11, for example the current(“generated current”) equivalent to 2× reference current is provided tothe circuit 13 from the terminal. The circuit 13 then distributes thedrive current (e.g., the current equivalent to 2× reference current)based on the generated current to the corresponding circuit of thecircuits 17-19.

In any of the sources 122-124, when both of the switch elements turn onby the changeover signal from the circuit 11, for example the current(“generated current”) equivalent to 3× reference current is provided tothe circuit 13 from the terminal. The circuit 13 then distributes thedrive current (e.g., the current equivalent to 3× reference current)based on the generated current to the corresponding circuit of thecircuits 17-19.

On the other hand, the source 121 provides for example the current(“generated current”) equivalent to the reference current to the circuit13 from the terminal T121 regardless of the changeover signal from thecircuit 11. The circuit 13 then distributes the drive current (e.g., thecurrent equivalent to the reference current) based on the generatedcurrent to the I/V conversion circuit 16. Since the voltage signal ofthe circuit 16 is amplified by the voltage amplification circuit 17,there is no need to expand the dynamic range of the circuit 16. On thecontrary, if the drive current to the circuit 16 was changed over, thevoltage signal of the circuit 16 might fluctuate. Therefore, the drivecurrent to the circuit 16 is fixed.

As described above, since the drive current to each of the circuits17-19 can be individually changed over based on the changeover signal,the drive current can be reduced to low level such as a few μA or 10 snA. For example, by changing over the drive current to each of thecircuits 17-19 based on variation of factor such as power voltage orambient temperature, the drive current can be appropriately reduced inaccordance with the variation. Expanding upon this, in a normal modewhen both of the switch elements in each of the sources 122-124 are offstate, when the variation causes operation of the circuits to beunstable, by turning the switch elements on one after another based onthe variation, the operation can be kept in stable state. As stillanother example, when a battery is utilized as a power source, sincebattery voltage will be varied (decreased) as time passed, by turningthe switch elements on one after another based on the variation, theoperation can be kept in stable state. On the other hand, when a fixedvoltage source except the battery is utilized, the operation of thecircuit (e.g., the circuit 17) which requires comparatively largercurrent can be kept in stable state by setting the drive current to thecircuit larger. Current consumption in each of the other circuits (e.g.,the circuits 18 and 19) can be reduced by setting its drive currentlower.

Moreover, since the fixed drive current is distributed to the circuit16, influence of current changeover in the circuit 16 can be excluded.Therefore the performance or behavior of the circuit 16 can be kept instable state, while current consumption of the circuits 17-19 can bereduced because the variable drive current is distributed to each of thecircuits 17-19.

In an alternate embodiment, the distribution circuit 13 distributes thedrive current to the circuits 16 and 19 based on the current from thefixed current source. The circuit 13 also distributes the drive currentto the circuits 17 and 18 based on the current from the variable currentsources. The circuit 19 comprises a means which is prohibited fromissuing the output signal when a pulse width from the circuit 18 is morenarrow than a prescribed width. This width is decided by the drivecurrent in order to prevent false detection. If drive current to thecircuit 16 was changed over, voltage of the circuit 16 would slightlyvary. The voltage with the slight variation is then amplified by thecircuit 17 and therefore the performance or behavior of the circuit 16could be unstable. If drive current to the circuit 19 was changed over,the prescribed width would be changed and therefore output signal offalse detection could be issued. For these reasons, it is desirable tofix drive current to each of the circuits 16 and 19.

In another alternate embodiment, the distribution circuit 13 as shown inFIG. 5 distributes the drive current to the circuits 16 and thedifferential stage 170 a of the circuit 17 based on the current from thefixed current source. The circuit 13 also distributes the drive currentto the output stage 170 b of the circuit 17 and circuits 18 and 19 basedon the current from the variable current sources. Thus, by distributingthe fixed dive current to the differential stage 170 a, operating point(offset) of the circuit 17 can be kept in stable state. Therefore,current consumption can be reduced while keeping the performance orbehavior of the circuit 16 and 17 in stable state in accordance with theabove-mentioned variation.

In this alternate embodiment, the drive current to the output stage 170b and circuits 18 and 19 is set to comparatively smaller current inorder to save power. Since objective performance cannot be obtained whenthe drive current to the output stage 170 b is reduced due to reductionof power voltage, the performance of the circuit 17 can be preferablymaintained by increasing the drive current to the output stage 170 b.

FIG. 6 shows an infrared detecting device B of a second embodimentaccording to the present invention.

The device B is characterized by a drive power supply circuit 20compared to the device A being different in that the drive power supplycircuit 20 is controlled by external signals.

The circuit 20 comprises a current changeover circuit 21, a currentgenerating circuit 22 and a distribution circuit 23. The circuit 20 alsosupplies a drive current to each of signal circuits comprised ofcircuits 26-29.

The current changeover circuit 21 as shown in FIG. 7 is constructed withinput terminals T211-T213, PMOS transistors 211-214 and a NMOStransistor 215. The PMOS transistors 211-213 are connected between thevoltage source and terminals T211-T213 respectively. Each gate of thesetransistors 211-213 is connected to gate and drain of the PMOStransistor 214 whose source is connected to the voltage source. The NMOStransistor 215 is connected between the gate and drain of the transistor214 and ground.

The current generating circuit 22 comprises a common variable currentsource 222 as a characteristic of the embodiment in addition tocomprising a reference current source 220 and a fixed current source 221as well as the circuit 12 of the device A. The variable current source222 further comprises a NMOS transistor 222 e and a switch element(e.g., PMOS transistor) 222 h as compared with the variable currentsource 122. Control terminals (gates) of the elements 222 f-222 h areconnected to the terminals T211-T213 respectively. Gate of the NMOStransistor 215 is connected to the drain and the gate of the NMOStransistor 221 a.

The distribution circuit 23 comprises a common current mirror circuit232 as another characteristic of the embodiment in addition tocomprising a current mirror circuit 231 as well as the circuit 13 of thedevice A. The current mirror circuit 232 further comprises a PMOStransistor 232 c whose drain is connected to the detection circuit 28and a PMOS transistor 232 d whose drain is connected to the outputcircuit 29 as compared with the current mirror circuit 132.

The circuit 20 is also set to deliver the minimum drive current to thecircuits 27-29 when the terminals T211-T213 are opened. In this case,since each changeover signal to the circuit 222 must be decided, thereis a need to pull up or down transistors of the circuit 21. In anexample of FIG. 7, each electric potential of the terminals T211-T213 ispulled up by the reference current from the reference current source 220in order to save power. Especially, in case the device B is mounted intoan IC, small-sized devices with multi-voltage (up to eight-way) can berealized by opening or grounding the terminals T211-T213 usingtechnology such as wirebonding.

According to the device B, drive current to the circuits 27-29 can bechanged over up to eight-way by providing the external signal of high orlow level to each of the terminals T211-T213, and therefore currentconsumption can be appropriately reduced.

When at least a battery of 1.5 V is utilized as a power source, drivecurrent to the circuits 27-29 can be set so that current consumption isoptimized by adjusting the external signals to the terminals T211-T213based on the number of the batteries.

FIG. 8 shows a part of an infrared detecting device C of a thirdembodiment according to the present invention.

The device C is characterized by a current changeover circuit 31 whichissues changeover signals to variable current sources 322-324 of acurrent generating circuit 32 based on power voltage.

The current changeover circuit 31 is comprised of resistors 311 and 312and NOT circuits 313 and 314. The resistors 311 and 312 are for exampleresistors (e.g., non-doped polysilicon) with high resistance (10 sMOhms) for saving power and detect divided voltage as the power voltage.The NOT circuits 313 and 314 have different thresholds and issue thechangeover signals in accordance with the divided voltage. For example,the threshold of the NOT circuit 313 is set to be higher than that ofthe NOT circuit 314. The NOT circuit 313 provides the changeover signalto one of the switch elements in each of the variable current sources322-324, while the NOT circuit 314 provides the changeover signal toanother of the switch elements in each of the sources 322-324.

The operation of the infrared detecting device C is now explained. Whenthe divided voltage detected by the resistors 311 and 312 is higher thanboth of the thresholds of the circuits 313 and 314, these circuitsprovide the changeover signals of Low level to the sources 322-324.Since the switch elements in each of the sources 322-324 then turn off,the drive power supply circuit provides for example the drive currentequivalent to the reference current for the voltage amplificationcircuit, the detection circuit and the output circuit.

When the divided voltage detected by the resistors 311 and 312 is lowerthan the threshold of the circuit 313 and higher than the threshold ofthe circuit 314, the circuits 313 and 314 provide the changeover signalsof High and Low level to the sources 322-324 respectively. Since theswitch elements in each of the sources 322-324 then turn on and off, thedrive power supply circuit provides for example the drive currentequivalent to 2× reference current for the voltage amplificationcircuit, the detection circuit and the output circuit.

When the divided voltage detected by the resistors 311 and 312 is lowerthan both of the thresholds of the circuits 313 and 314, these circuitsprovide the changeover signals of High level to the sources 322-324.Since the switch elements in each of the sources 322-324 then turn on,the drive power supply circuit provides for example the drive currentequivalent to 3× reference current for the voltage amplificationcircuit, the detection circuit and the output circuit.

Therefore, when the drive current to the signal circuits as shown inFIG. 9 is varied (decreased) due to the variation (reduction) of thepower voltage, the drive current to each of the voltage amplificationcircuit, the detection circuit and the output circuit is adjusted(increased) by two-step operation. As a result, the drive current can beconverged within a prescribed range of optimal current consumption overa prescribed variation range of the power voltage, and the drive currentcan be preferably reduced based on the variation of the power voltage.

In an alternate embodiment, the current changeover circuit 31 comprisesat least three NOT circuits. The circuit 31 also issues at least fourkinds of changeover signals. The current generating circuit and thedistribution circuit then provide at least four kinds of drive currentsto the voltage amplification circuit, the detection circuit and theoutput circuit according to the changeover signals from the circuit 31.

In another alternate embodiment, the current changeover circuit 31comprises resistors 311 and 312 with different temperaturecharacteristics. In the construction of FIG. 8, a resistor (e.g.,non-doped polysilicon) with high resistance and large negativetemperature characteristics is used as the resistor 311. In this case,since the divided voltage decreases while the resistance of the resistor311 becomes high as ambient temperature decreases, the switch elementsin each of the sources 322-324 are turn on one after another so as tostep the drive current up. Therefore, when the drive current to thesignal circuits as shown in FIG. 10 is varied (decreased) due to thevariation (increase) of ambient temperature, the drive current to eachof the voltage amplification circuit, the detection circuit and theoutput circuit is adjusted (increased) by two-step operation. As aresult, the drive current can be converged within a prescribed range ofoptimal current consumption over a prescribed variation range of ambienttemperature, and the drive current can be preferably reduced based onthe variation in ambient temperature.

FIG. 11 shows an infrared detecting device D of a fourth embodimentaccording to the present invention.

The device D is characterized by comprising a battery as a power source(not shown in FIG. 11), a mode changeover circuit 40D, a currentchangeover circuit 41 and a suppression circuit 44 in addition tocomprising a pyroelectric element 45, an I/V conversion circuit 46, avoltage amplification circuit 47, a detection circuit 48 and an outputcircuit 49 as well as the device A.

The mode changeover circuit 40D further comprises a holding circuit 400while comprising a current generating circuit 42 and a distributioncircuit 43 as well as the device A. The holding circuit 400 as shown inFIG. 12 holds state of output signal S49 of the output circuit 49 for aprescribed time period T41. The state of S49 is held from a point intime (fall time of S48) when components-amplified voltage V47 by thecircuit 47 becomes equal to a prescribed detection threshold voltageV481 or V482 of the detection circuit 48 or closer to a reference level(“offset” by bias voltage) Vb than the detection threshold voltage.Hereinafter the period T41 is also referred to as a “holding period”T41.

The current changeover circuit 41 provides a changeover signal to one ofthe switch elements in each variable current source of the currentgenerating circuit 42. The circuit 41 also provides another changeoversignal to another of the switch elements. One of these changeoversignals is further explained.

The circuit 41 as shown in FIG. 12 provides a first (Low) or second(High) changeover signal as the changeover signal S411 to each variablecurrent source. That is, the circuit 41 issues the first changeoversignal from an end point in time of the holding period T41. This signalis issued while the voltage V47 is equal to a prescribed transitionthreshold voltage V411 or V412′ or closer to reference level Vb than thetransition threshold voltage. The voltage V411 or V412 is set, to becloser to the reference level Vb than the detection threshold voltage.The circuit 41 also issues the second changeover signal. This signal isissued while the voltage V47 is further from the reference level Vb thanthe transition threshold voltage. The second changeover signal is alsoheld during the holding period T41.

Therefore the each variable current source steps the variable currentdown to a current (hereinafter referred to as a “power-saving current”)smaller than a rated current of the different currents and keeps thepower-saving current while the first changeover signal is issued. On theother hand, the each variable current source steps the variable currentup to the rated current and keeps the rated current while the secondchangeover signal is issued. The each variable current source also stepsthe variable current up or down according to the another changeoversignal (not shown in FIG. 12) different from the signal S411.

The suppression circuit 44 starts suppression of output of any circuitor circuits included in the signal circuits (circuits 46-49) in order tosuppress the output signal. The suppression is started from a startpoint in time on or before which the each variable current source stepsdown the variable current. The output of the circuit is suppressed sothat an output signal which represents non-detection of a human body isissued from the output circuit 49. The circuit 44 as shown in FIG. 12also releases the suppression after a prescribed time period(hereinafter referred to as a “suppressing period”) T42 which includes apoint in time on which the variable current is stepped down.

In an example of FIG. 11, the circuit 44 is constructed with a resistor441, a constant voltage supply circuit 442, a switch (e.g.,semiconductor switch element) 443 and a switch controlling circuit 444.The resistor 441 is connected in series between an output end of thevoltage amplification circuit 47 and an input end of the detectioncircuit 48. The constant voltage supply circuit 442 supplies a constantvoltage between the resistor 441 and the in put end of the detectioncircuit 48 through the switch 443. This switch 443 is connected betweenfrom an output end of the constant voltage supply circuit 442 toresistor 441 and the input end of the detection circuit 48. The switch443 also opens or closes a pathway from the circuit 442 to resistor 441and the circuit 48 in response to OFF or ON signal respectively. Theswitch controlling circuit 444 as shown in FIG. 12 provides the ONsignal as signal S444 to the switch 443 from the above-mentioned startpoint. The circuit 444 also provides the OFF signal as the signal S444to the switch 443 after the suppressing period T42. In a words, thecircuit 444 starts suppression of an output of the voltage amplificationcircuit 47 from the start point in time on which the each variablecurrent source steps down the variable current. And the circuit 444releases the suppression after the suppressing period T42 from the startpoint.

The operation of the infrared detecting device D is now explained. Inoperation mode, even if the components-amplified voltage V47 convergesto within the window threshold range V481-V482, output signal S49 whichrepresents a detection of a human body is held for the holding periodT41. When the voltage V47 then converges to within the window thresholdrange V411-V412, the first changeover signal is issued at the end pointof the holding period T41 from the current changeover circuit 41 whilethe ON signal S444 is issued from the switch controlling circuit 444. Asa result, the drive current is stepped down to the power-saving currentand kept to the power-saving current while the output of the voltageamplification circuit 47 is suppressed at the constant voltage of thecircuit 442 for the suppressing period T42. After this period T42, theOFF signal S444 is issued from the switch controlling circuit 444.Therefore, the suppression of the output of the circuit 47 is released.

In this stand-by mode, when the voltage V47 becomes less or more thanthe window threshold range V411-V412, the second changeover signal isissued from the current changeover circuit 41. Therefore, the drivecurrent is stepped up to the rated current and kept to the ratedcurrent. When the voltage V47 then becomes less or more than the windowthreshold range V481-V482, output signal S49 which represents adetection of a human body is issued from the output circuit 49.

Therefore, by setting the suppressing period T42 to a longer time period(e.g., about 1-2 seconds) than that in which the performance or behaviorof the circuit 47 becomes unstable it becomes possible to prevent falseoperation due to variation when the drive current is stepped down.

FIG. 13 shows a part of an infrared detecting device E of a fifthembodiment according to the present invention.

The device E is characterized by a suppression circuit 54 and differentonly in that the suppression circuit 54 is constructed with a switch(e.g., semiconductor switch element) 543 and a switch controllingcircuit 544 as compared with the device D.

The switch 543 is connected in parallel with a feedback resistor 571.This resistor 571 is connected between a positive input terminal and anoutput terminal of an operational amplifier 570 in a voltageamplification circuit 57. The switch 543 also opens or closes itsparallel pathway in response to OFF or ON signal respectively.

The switch controlling circuit 544 provides the ON signal to a controlterminal of the switch 543 from the above-mentioned start point (ref. Ontime of S444 in FIG. 12). The circuit 544 also provides the OFF signalto the control terminal of the switch 543 after the above-mentionedsuppressing period.

In this device E, an output of the voltage amplification circuit 57 issuppressed at 1× input voltage of the circuit 57 during the suppressingperiod. Therefore, by setting the suppressing period as well as thesuppressing period T42 it becomes possible to prevent false operationdue to variation when the drive current is stepped down.

FIG. 14 shows a part of an infrared detecting device F of a sixthembodiment according to the present invention.

The device F is characterized by a suppression circuit 64 which isconstructed with a resistor 641, a switch (e.g., semiconductor switchelement) 643, a constant voltage supply circuit 642 and a switchcontrolling circuit 644. As compared with the device D, the circuit 64has different circuit arrangement and different switch control function.

The resistor 641 prevents influence to an output signal of a voltageamplification circuit 67 when the switch 643 turns on.

The switch 643 is connected between an output end of the voltageamplification circuit 67 and an input end of a detection circuit 68. Theswitch 643 also opens or closes a pathway from the circuit 67 to thecircuit 68 in response to OFF or ON signal respectively.

The constant voltage supply circuit 642 supplies a constant voltagebetween the switch 643 and the detection circuit 68 through the resistor641.

The switch controlling circuit 644 as shown in FIG. 15 provides the OFFsignal as a signal S644 to a control terminal of the switch 643 from theabove-mentioned start point of a suppressing period T62. The circuit 644also provides the ON signal as the signal S644 to the control terminalof the switch 643 after the suppressing period T62.

In this device F, the pathway from the voltage amplification circuit 67to the detection circuit 68 is opened during the suppressing period T62.Therefore, by setting the suppressing period T62 as well as thesuppressing period T42 it becomes possible to prevent false operationdue to variation when the drive current is stepped down.

FIG. 16 shows a part of an infrared detecting device G of a seventhembodiment according to the present invention.

The device G is characterized by a suppression circuit 74 and differentonly in that the suppression circuit 74 is constructed with a constantvoltage supply circuit 742, a switch (e.g., semiconductor switchelement) 743 and a switch controlling circuit 744 as compared with thedevice D.

The constant voltage supply circuit 742 supplies a constant voltage toan input end of a detection circuit 78 through the switch 743.

The switch 743 is connected between from the constant voltage supplycircuit 742 and a voltage amplification circuit 77 to the detectioncircuit 78. The switch 743 closes or opens a pathway (hereinafterreferred to as a “first pathway”) between the constant voltage supplycircuit 742 and the detection circuit 78 in response to suppression orunsuppression signal respectively. The switch 743 also opens or closes apathway (hereinafter referred to as a “second pathway”) between thevoltage amplification circuit 77 and the detection circuit 78 inresponse to the suppression or the unsuppression signal respectively.

The switch controlling circuit 744 provides the suppression signal to acontrol terminal of the switch 743 from the above-mentioned start point.The circuit 744 provides the unsuppression signal to the controlterminal of the switch 743 after the above-mentioned suppressing period.

In this device G, the first and the second pathways are closed andopened during the suppressing period. Therefore, by setting thesuppressing period as well as the suppressing period T42 it becomespossible to prevent false operation due to variation when the drivecurrent is stepped down.

FIG. 17 shows a part of an infrared detecting device H of a eighthembodiment according to the present invention.

The device H is characterized by a suppression circuit 84 and differentonly in that the suppression circuit 84 is constructed with a switch(e.g., semiconductor switch element) 843 and a switch controllingcircuit 844 as compared with the device D.

The switch 843 is connected between an output end of a detection circuit88 and an input end of an output circuit 89. The switch 843 also opensor closes a pathway between the detection circuit 88 and the outputcircuit 89 in response to OFF or ON signal respectively.

The switch controlling circuit 844 provides the OFF signal to a controlterminal of the switch 843 from the above-mentioned start point. Thecircuit 844 also provides the ON signal to the control terminal of theswitch 843 after the above-mentioned suppressing period.

In this device H, the pathway is opened during the suppressing period.Therefore, by setting the suppressing period as well as the suppressingperiod T42 it becomes possible to prevent false operation due tovariation when the drive current is stepped down.

In an alternate embodiment, the switch controlling circuit 844 as shownin FIG. 18 generates a signal S8. This signal S8 becomes Low duringsuppressing period T82 and becomes High during the other time period.The circuit 844 then generates a signal S843 by logicaland of the signalS8 and a changeover signal S811 equivalent to the S411 in the FIG. 12.The circuit 844 then provides the signal S843 to the control terminal ofswitch 843.

FIG. 19 shows a part of an infrared detecting device J of a ninthembodiment according to the present invention.

The device J is characterized by a common variable current source 922 ofa current generating circuit 92 and a current changeover circuit 91 anddifferent in that the current changeover circuit 91 has different switchcontrol function as compared with the device D.

The current generating circuit 92 comprises the above-mentioned commonvariable current source 922 in addition to a reference current source920 and a fixed current source 921 with NMOS transistors 921 a and 921b. The common variable current source 922 is constructed with NMOStransistors M1-Mn and switch elements (e.g., semiconductor switchelement) SW2-SWn. The source 922 also provides variable current to acurrent mirror circuit 932 which is included in a distribution circuit93 and constructed with PMOS transistors 932 a-932 d as well as FIG. 7.

The current changeover circuit 91 provides a signals S943 as theabove-mentioned first and second changeover signal to each controlterminal of the switch elements SW2-SWn. The signals S943 includessignals S2-Sn (e.g., S2-S4) provided to the terminals of the switchelements SW2-SWn (e.g., SW2-SW4) respectively.

Expanding upon the above, the circuit 91 as shown in FIG. 20 issues thesecond changeover signals (sequential ON signals) S943 so that thevariable current source 922 increases variable current to the biggestrated current while stepping up from smallest current of the differentcurrents according to the second changeover signals. The circuit 91 alsoissues the first changeover signals (sequential OFF signals) S943 sothat the variable current source 922 decreases variable current to thesmallest current while stepping down from the rated current of thedifferent currents according to the first changeover signals.

In this device J, the variable current is increased or decreased bysequential step up or down (discrete up or down) operation which canreduce variation. Therefore, it becomes possible to preferably preventfalse operation due to variation when the drive current is increased ordecreased.

Although the present invention has been described with reference tocertain preferred embodiments, numerous modifications and variations canbe made by those skilled in the art without departing from the truespirit and scope of this invention.

For example, it should be appreciated that the suppression circuit maystart suppression of an output of a circuit included in the signalcircuits from a start point in time on or before which the each variablecurrent source steps “up” the variable current. In this case, the outputof the circuit is suppressed so that an output signal which represents“non-detection” of a human body is issued from the output circuit.

1. An infrared detecting device, comprising: a pyroelectric elementwhich generates a current signal based on incoming infrared radiation;an I/V conversion circuit which converts said current signal into avoltage signal; a voltage amplification circuit which selectivelyamplifies components with prescribed frequencies of said voltage signalto issue a components-amplified voltage; a detection circuit whichprovides a comparison between the components-amplified voltage and aprescribed detection threshold voltage to issue a detection signal ofthe infrared radiation; an output circuit which issues an output signalbased on to the detection signal; and a drive power supply circuit whichsupplies a drive current to each of signal circuits comprised of the I/Vconversion circuit, the voltage amplification circuit, the detectioncircuit and the output circuit; wherein said drive power supply circuitis comprised of; a current generating circuit which includes a referencecurrent source, a fixed current source and a variable current source,said reference current source being configured to generate a referencecurrent, said fixed current source being configured to provide a fixedcurrent based on said reference current, said variable current sourcebeing configured to provide a variable current varying with saidreference current; and a distribution circuit configured to distributethe drive current to a part of said signal circuits based on the currentfrom said fixed current source, said distribution circuit beingconfigured to distribute the drive current to the remaining part of saidsignal circuits based on the current from said variable current source.2. The infrared detecting device of claim 1, wherein said drive powersupply circuit comprises a plural of the variable current source, eachof said variable current sources being individually connected to eachcircuit of said remaining part of the signal circuits.
 3. The infrareddetecting device of claim 1, wherein: said drive power supply circuitcomprises a terminal for receiving a changeover signal; and saidvariable current source steps the variable current up or down to any ofprescribed different currents in accordance with the changeover signalreceived at said terminal.
 4. The infrared detecting device of claim 1,wherein said variable current source steps the variable current up ordown to any of prescribed different currents based on variation of powervoltage.
 5. The infrared detecting device of claim 1, wherein saidvariable current source steps the variable current up or down to any ofprescribed different currents based on variation in ambient temperature.6. The infrared detecting device of claim 1, wherein: the voltageamplification circuit comprises a differential stage and an outputstage; the distribution circuit distributes the drive current to thedifferential stage or the output stage based on the current from saidvariable current source, or distributes same or different current as thedrive current to the differential stage and the output stage based onthe current from said variable current source.
 7. The infrared detectingdevice of claim 1, further comprising a suppression circuit, wherein:said drive power supply circuit comprises a current changeover circuit,said current changeover circuit being configured to provide a firstchangeover signal to said variable current source when saidcomponents-amplified voltage is closer to a reference level than atransition threshold voltage, said transition threshold voltage beingset to be closer to the reference level than said detection thresholdvoltage, said current changeover circuit being configured to provide asecond changeover signal to said variable current source when saidcomponents-amplified voltage is further from the reference level thanthe transition threshold voltage; said variable current sourceconfigured to step the variable current down to a current smaller than arated current of prescribed different currents based on said firstchangeover signal, said variable current source being configured to stepthe variable current up to the rated current based on said secondchangeover signal; and said suppression circuit configured to startsuppression of output of any circuit or circuits included in said signalcircuits in order to suppress said output signal from a start point intime on or before which said variable current source steps up or downthe variable current, said suppression circuit being configured torelease the suppression after a prescribed time period.
 8. The infrareddetecting device of claim 7, wherein said suppression circuit comprises:a resistor which is connected in series between said voltageamplification circuit and said detection circuit; a constant voltagesupply circuit for supplying a constant voltage between said resistorand said detection circuit; a switch that is connected between from saidconstant voltage supply circuit to said resistor and said detectioncircuit, said switch being configured to open or close a pathway fromsaid constant voltage supply circuit to said resistor and said detectioncircuit in response to OFF or ON signal respectively; and a switchcontrolling circuit configured to provide the ON signal to said switchfrom said start point, said switch controlling circuit being configuredto provide the OFF signal to said switch after said time period.
 9. Theinfrared detecting device of claim 7, wherein: said voltageamplification circuit comprises an operational amplifier and a feedbackresistor, said operational amplifier having a positive input terminal, anegative input terminal and an output terminal, said feedback resistorbeing connected between said output terminal and one of said inputterminals; and said suppression circuit comprises a switch and a switchcontrolling circuit, said switch being connected in parallel with saidfeedback resistor, said switch being configured to open or close itsparallel pathway in response to OFF or ON signal respectively, saidswitch controlling circuit being configured to provide the ON signal tosaid switch from said start point, said switch controlling circuit beingconfigured to provide the OFF signal to said switch after said timeperiod.
 10. The infrared detecting device of claim 7, wherein saidsuppression circuit comprises: a resistor; a switch that is connectedbetween said voltage amplification circuit and said detection circuit,said switch being configured to open or close a pathway from saidvoltage amplification circuit to said detection circuit in response toOFF or ON signal respectively; a constant voltage supply circuit whichsupplies a constant voltage between said switch and said detectioncircuit through said resistor; and a switch controlling circuitconfigured to provide the OFF signal to said switch from said startpoint, said switch controlling circuit being configured to provide theON signal to said switch after said time period.
 11. The infrareddetecting device of claim 7, wherein said suppression circuit comprises:a constant voltage supply circuit for supplying a constant voltage tosaid detection circuit; a switch that is connected between from saidconstant voltage supply circuit and said voltage amplification circuitto said detection circuit, said switch being configured to close or opena pathway between said constant voltage supply circuit and saiddetection circuit in response to suppression or unsuppression signalrespectively, said switch being configured to open or close a pathwaybetween said voltage amplification circuit and said detection circuit inresponse to the suppression or the unsuppression signal respectively;and a switch controlling circuit configured to provide the suppressionsignal to said switch from said start point, said switch controllingcircuit being configured to provide the unsuppression signal to saidswitch after said time period.
 12. The infrared detecting device ofclaim 7, wherein said suppression circuit comprises: a switch that isconnected between said detection circuit and said output circuit, saidswitch being configured to open or close a pathway between saiddetection circuit and said output circuit in response to OFF or ONsignal respectively; and a switch controlling circuit configured toprovide the OFF signal to said switch from said start point, said switchcontrolling circuit being configured to provide the ON signal to saidswitch after said time period.
 13. The infrared detecting device ofclaim 7, wherein said switch controlling circuit issues: said secondchangeover signal so that said variable current source increases thevariable current to the biggest rated current while stepping up fromsmallest current of the different currents according to the secondchangeover signal, and said first changeover signal so that saidvariable current source decreases the variable current to the smallestcurrent while stepping down from the rated current of the differentcurrents according to the first changeover signal.